AMERICAN HYDROIDS. 121 



projections behind each hydrocladial internode form a feature that I have not seen elsewhere. 

 The anterior keel far surpasses any other that is found among the American Plumularida'. 

 Type. In the Museum of Yale University. 



LYTOCARPUS (Kirehenpauer) Allman 1 (modified). 



Li/toi'iir/iiii (Subgeuus) KiucnENPAi'ER, Ueber die Hydroidenfamilie Plunmlaridae, 1872, p. 27. 

 Lytocarpus HALE, The Genera of the PlnmolariidiB, 1886, p. l.~>. 

 \,'mat<n>lioniK CI.AHKE, Bull. Mus. Coiup. Xool., 1879, V, Xo. 101, p. 248. 

 FEWKKS, Bull. Mus. Cornp. Zool., 1881, VIII, No. 7, p. 136. 



Tr<>i>li.<some. Stem fascicled; hydrothecal margin strongly toothed or sinuous; mesial 

 nematophore usually (always in the American species) with two openings, a prominent perforated 

 process at the base of each hydrocladiuui, and broad triangular cauline nematophores. 



Gonoxome. Gonaiigia borne on hydrocladia which are modified so as to form protective 

 branchlets, often aggregated into a pseudocorbula, which differs from a real corbula in the 

 fact that its leaves are formed by modified hydrocladia instead of appendages to hydrocladia, 

 as in the genus Ai/lnoplivnut. The gouangia take the place of hydrotheca' in the species which 

 I have examined, and there is a hydrotheca on the proximal part of each protective branch. 



In his admirable discussion of the genera of the Plumularidu', Bale clearly shows that that 

 portion of the genus Lytocitrptix as defined by Allman, which is typified by Aglaophenia 

 iin/rio)iJn/Iliim is out of place in Lytocarpus, as its gonosome forms a real corbula in the shape 

 of a highly modified hydrocladium. I have been so fortunate as to discover a species closely 

 related to Nematophorun r/i-itndis Clarke, the gouosome of which -has been hitherto unknown, 

 which agrees well with that of Fewkes's genus Pleurocarpa, in which the gonosome is a 

 pseudocorbula formed of the proximal part of a branch, with hydrocladia transformed into 

 protective brauchlets bearing gouangia. It differs from Doctor Fewkes's description, 2 however, in 

 not having true hydrothecm on the stem, but having one at the base of each protective 

 branchlet. It is somewhat difficult to determine the true position of these hydrotheca', and I 

 am inclined to think that we have here no exception to the otherwise invariable rule that 

 there are no cauline hydrotheca/ among the Statoplea. 



The nematophores on the protective branchlets in Lytocarpm grandin are long, tubular, and 

 do not occur on all sides of the branchlet. The latter is divided into regular internodes, the first 

 of which bears a hydrotheca, the second and several succeeding ones bear the mesial and 

 supracalycine uematophores, the place of the hydrotheca being occupied by a goiiangium. The 

 distal portion of the branchlet bears a close resemblance to an unbranched phylactogonium of the 

 genus Cladocarpits. 



The uematophores in this genus are often very large and bear exceedingly large neinatocysts, 

 which are capable of inflicting severe pain when brought in contact with the skin. This is the 

 only plumularian, so far as I know, that is capable of sensibly irritating the human skin. 



My reason for doing away with the genus 1'lcnrocarpa of Fewkes is twofold. In the first 

 place, it is the same as the genus Nematophorus of Clarke, which has the precedence. In the 

 second place, it seems evident that the protective branchlets are really altered hydrocladia, as 

 maintained by Fewkes, aud thus the structure is inseparable from that found in the genus 

 Lytocarpus as defined by Allman. The fact that there are true hydrocladia beyond the pseudo- 

 corbula does not at all invalidate this position, as exactly the same thing is found in Lytocarpus 

 racvniiferiis Allman. 



In regard to the abandonment of the geuus Nematophorttx of Clarke, that genus was based on 

 the presence of the peculiar perforated protuberances on the bases of the hydrocladia. These 

 structures, however, are found in less prominent form in very many plumularians, indeed in most 

 genera of the Statoplea, and especially in Lytocarpux. The genus yematopliorus being in my 

 opinion, untenable, its single species, with other closely allied forms, is here referred to the genus 

 Lytocarpus which Allrnau raised to generic rank from the old subgeuus Lytomrpta of Kircheupauer. 



1 Challenger Report, Hydroidn, Pt. 1, 1883, p. 40. 



2 Since the above was written I have been permitted to examine Doctor Fewkes's type of this <;eniis, and find no 

 hydrothec;c on the stem of the pseudocorbula, and one at the base of each protective branchlet. 



